1. Field of the Invention
The present invention relates to a valve timing control device for modifying the opening and closing timing of the intake and exhaust valves in an internal-combustion engine (hereafter, referred as an engine) according to any operating condition.
2. Description of the Prior Art
Conventional valve timing control devices are known as shown in FIG. 1 to FIG. 4. FIG. 1 is a lateral cross sectional view of an internal construction of the conventional vane-type valve timing control device. FIG. 2 is a longitudinal cross sectional view taken along lines Axe2x80x94A of FIG. 1. FIG. 3 is a longitudinal cross sectional view of the conventional lock-release mechanism of FIG. 2. FIG. 4 is an enlarged perspective view of main points of the lock-release mechanism in the conventional valve timing control device of FIG. 1. FIG. 5 is a graph of relation defined between stroke in operation of a lock member in the lock-release mechanism of FIG. 2 and FIG. 3 and oil pressure. In FIG. 2, a right hand direction denotes forward, and a left hand direction denotes backward. In FIG. 2 and FIG. 3, a lower side denotes forward, and an upper side denotes backward.
In the drawings, reference numeral 1 denotes a first rotor which connects with a crankshaft (not shown) of the engine through chains (not shown) or belts (not shown) to rotate in synchronization with the crankshaft (not shown). The first rotor includes a sprocket 2, a case 3 and a cover 4, which are integrated with a threaded member 5 such as a bolt and so on. The sprocket 2 rotates in conjunction with the crankshaft (not shown). The case 3 has a plurality of shoes 3a, which are projected from an inner portion of the case 3 to constitute a plurality of oil hydraulic pressure chambers between the shoes 3a. The cover 4 covers the oil hydraulic pressure chambers constituted by the shoes 3a of the case 3.
A rotor (second rotor) 6 is arranged within the case 3, and allows relative rotation with respect to the first rotor 1. The rotor 6 is fixedly integrated with a camshaft 7 by using a threaded member 8 such as a bolt and so on, and the camshaft 7 relates to open/close of an intake valve or an exhaust valve. The rotor 6 has a plurality of vanes 6a of dividing the hydraulic pressure chambers above into an advance side oil hydraulic pressure chamber 9 and a retardation side oil hydraulic pressure chamber 10. A first oil path .(pressure supply path) 11 and a second oil path (pressure supply path) 12 are arranged within the camshaft 7. The first oil path 11 performs supply of oil hydraulic pressure to and discharge thereof from the advance side oil hydraulic pressure chamber 9. The second oil path 12 performs supply of oil hydraulic pressure to and discharge thereof from the retardation side oil hydraulic pressure chamber 10.
Seal means 13 are arranged on both of front ends of the shoes 3a of the case 3 and the vanes 6a of the rotor 6, respectively. The respective seal means 13 prevents leakage of oil between the both of the oil hydraulic pressure chambers 9 and 10. The seal means 13 includes a seal member 13a of sliding on an inner wall face of the oil hydraulic pressure chambers 9 and 10, and a plate spring 13b of biasing the seal member 13a toward the inner wall face.
An accommodation hole 14 is arranged at one of the vanes 6a of the rotor 6 which acts as the second rotor. A lock pin (lock member, lock mechanism) 15 having a cylindrical shape is accommodated in the hole 14 to restrict relative rotation of the first rotor 1 and the second rotor. Since oil hydraulic pressure in the valve timing control device is reduced on starting the engine, the rotor 6 vibrates in the rotational direction by a cam load applied to a cam (not shown) integrated with the camshaft 7 to repeat contact and separation between the first and second rotors. Therefore, the lock pin 15 is biased by an biasing member (lock mechanism) 16 such as coil springs to engage in an engagement hole will be explained hereafter, the biasing member 16 being arranged between a rear wall of the accommodation hole 14 and the lock pin 15. A discharge hole (release mechanism) is formed with the accommodation hole 14 to discharge a backward pressure of the lock pin 15.
On the other hand, an, engagement hole 18 is formed at the sprocket 2 which acts as the first rotor to allow insertion of the lock pin 15 when the rotor 6 positions at the most retardation with respect to the first rotor 1.
A valve 19 is arranged at the vane 6a having the accommodation hole 14. The valve 19 supplies selectively higher oil hydraulic pressure in the advance side oil hydraulic pressure chamber 9 and the retardation side oil hydraulic pressure chamber 10 to the engagement hole 18 to release engagement (hereafter, referred as lock) between the engagement hole and the lock pin 15. The valve (release mechanism) 19 communicates with the engagement hole 18 through a first release oil hydraulic supply path (release mechanism) 20 formed in the said vane 6a of the rotor 6 and a second release oil hydraulic supply path (release mechanism) 21 formed at the sprocket 2. The valve 19 communicates with the advance side oil hydraulic pressure chamber 9 through an advance side pressure partition path (release mechanism) 22, and communicates with the retardation side oil hydraulic pressure chamber 10 through a retardation side pressure partition path (release mechanism) 23.
Next, a release operation will be explained.
In a release operation, oil hydraulic pressure is supplied from an oil pump (not shown) to the engagement hole 18 through the chamber 9 or the chamber 10, the valve 19, the first release oil hydraulic supply path 20 and the second release oil hydraulic supply path 21. Release oil pressure is supplied to a space defined between an inner wall of the engagement hole 18 and an outer wall of the lock pin 15 within the engagement hole 18 to press the lock pin 15 against the biasing force of the biasing member 16. Thus, the lock pin 15 is moved backward in the accommodation hole 14 to release from the engagement hole 18. Backward pressure of the lock pin 15 is discharged from the accommodation hole 14 through the discharge hole 17 to the outside of the valve timing control device. A front end of the lock pin 15 released from the engagement hole 18 is accommodated in the accommodation hole 14 to allow free rotation between the first and second rotors.
Since an area subjected to oil pressure is constant from a locked state of the lock pin 15 to the end of a released state, a discharge speed of the backward pressure is also constant. Since strokes in the operation of the lock pin 15 are determined by the biasing force of the biasing member 16 and the oil pressure force, a one-on-one relation is established in the stroke and applied oil pressure. Therefore, release oil pressure is equal to holding-release oil pressure of holding the released state.
Incidentally, when the engine is stopped, oil in the advance side oil hydraulic pressure chamber 9 and the retardation side oil hydraulic pressure chamber 10 moves downwardly to an oil-pan (not shown) through the first and second oil path 11 and 12 and so on. Therefore, air accumulates in pipe arrangement such as the respective oil hydraulic pressure chambers and the respective oil paths. When the engine is restarted with the state above, oil hydraulic pressure rises by the oil pump (not shown) and simultaneously accumulated air in the pipe arrangement is discharged at once. Thus, the air-mixing oil is applied in the valve timing control device to release instantly the lock pin 15 from the engagement hole 18.
However, the following problems result from the above structure for a conventional valve timing control device.
When the air-mixing oil releases the lock on starting the engine, the oil hydraulic pressure in the advance side oil hydraulic pressure chamber 10 and the retardation side oil hydraulic pressure chamber 11 cannot absorb the cam load described above. Since the first rotor 1 and the second rotor repeat contact and separation there-between, beat noise (abnormal noise) necessarily results.
Other conventional valve timing control devices are known as disclosed in JP-A-1998/159519, for example. The device has a release path formed in a release oil hydraulic pressure chamber defined between a shoulder of a lock pin and an accommodation hole, and the release path discharges only air mixed in oil to the outside. Thus, the device solves the problem that engagement of the lock pin is accidentally released by the air mixed in oil before reaching a sufficient oil pressure. However, since oil and air (pressurized fluid) guided to the release path pass through the release oil hydraulic pressure chamber, air is slightly mixed with the oil acting on the lock pin. In this case, the release path is sealed by oil components having little effect on a release operation. Therefore, since there is a possibility of accidental release of the lock before reaching a sufficient oil pressure, this device does not solve the problem above.
Accordingly, it is an object of the present invention to provide a valve timing control device, which prevents the occurrence of beat noise (abnormal noise) in a release operation resulting from the air-mixing oil on starting the engine.
In order to achieve the object of the present invention, a valve timing control device comprises a first rotor of rotating in synchronization with a crankshaft of an internal combustion engine, the first rotor having a plurality of shoes inside thereof; a second rotor fixed on an end of an intake camshaft or an exhaust camshaft of the internal combustion engine and rotatably arranged in the first rotor, the second rotor having a plurality of vanes on the outside; an advance side oil hydraulic pressure chamber and a retardation side oil hydraulic pressure chamber defined between the vanes of the second rotor and the shoes of the first rotor; a lock member of locking the first and second rotors at a required angle which any one of the rotors forms with the other; an accommodation hole arranged at the second rotor, accommodating the lock member and biasing member for biasing the lock member, the accommodation hole having a discharge hole for discharging backward pressure of the lock member; an engagement hole arranged at the first rotor, allowing insertion of the lock member, the engagement hole having a release oil hydraulic supply path for supplying release oil pressure; an advance side pressure partition path communicating with the advance side oil hydraulic pressure chamber; a retardation side pressure partition path communicating with the retardation side oil hydraulic pressure chamber; and a purge path communicating at least one of the advance side oil hydraulic pressure chamber, the retardation side oil hydraulic pressure chamber, the advance side pressure partition path and the retardation side pressure partition path with ambient air. Thus, air or air-mixing oil, which is used as a first pressure in a release operation on starting the engine, can be positively discharged to the outside. It is not necessary to use all the first pressure for the release operation, and the lock member can be released after applying oil hydraulic pressure which is able to control the valve timing control device. Therefore, it can prevent the occurrence of beat noise (abnormal noise).
The purge path may be arranged in the accommodation hole functioning as a backward chamber of the lock member to communicate with at least one of the advance side oil hydraulic pressure chamber, the retardation side oil hydraulic pressure chamber, the advance side pressure partition path and the retardation side pressure partition path. Thus, the oil pressure of air-mixing oil, which is supplied to the accommodation hole through the purge path, acts on against release oil pressure supplied to the engagement hole through release oil hydraulic supply path. Therefore, the release operation can be delayed until applying oil hydraulic pressure which is able to control the valve timing control device to prevent the occurrence of beat noise (abnormal noise).
The device may further comprise a drain path communicating the purge path with ambient air, wherein the drain path and the purge path are arranged in the accommodation hole which functions as a backward chamber of the lock member, and wherein the purge path communicates with at least one of the advance side oil hydraulic pressure chamber, the retardation side oil hydraulic pressure chamber, the advance side pressure partition path and the retardation side pressure partition path. Thus, the oil pressure of air-mixing oil, which is supplied to the accommodation hole through the purge path, acts against release oil pressure supplied to the engagement hole through release oil hydraulic supply path. Therefore, the release operation can be delayed to prevent the occurrence of beat noise (abnormal noise). Moreover, air-mixing oil can be quickly discharged in the release operation through the drain path.
The purge path may communicate the retardation side oil hydraulic pressure chamber or the retardation side pressure partition path with ambient air. Thus, oil pressure of air-mixing oil is supplied from the retardation side oil hydraulic pressure chamber or the retardation side oil pressure partition path to the accommodation hole through the purge path, and acts on against release oil pressure supplied to the engagement hole through release oil hydraulic supply path. As a result, the release operation can be delayed.
The purge path may be connected to the accommodation hole so as to be closed by the lock member in a release operation. Thus, oil supply from the purge path to the accommodation hole can be closed in the release operation after discharging the air-mixing oil to prevent residual oil pressure in the accommodation hole.
The purge path may be connected to the accommodation hole during a period from the start of lock operation to that of required stroke operation of the lock member. Thus, oil supply from the purge path to the accommodation hole can be closed during the period to prevent residual oil pressure in the accommodation hole.
The device may further comprise a choke arranged in the purge path, wherein the choke may narrow an opening area of the purge path. Thus, path resistance can be increased to restrict passing of non-compressive oil with high viscosity through the purge path to allow selectively passing of compressive air with low viscosity through it.
An opening area of the purge path may be narrower than that of a pressure supply path communicating with the advance side oil hydraulic pressure chamber and the retardation side oil hydraulic pressure chamber. Thus, oil pressure in the advance side oil hydraulic pressure chamber and the retardation side oil hydraulic pressure chamber can be held at a constant level.
An opening area of the purge path may be generally equal to, or may be wider than that of the discharge hole or the drain path. Thus, oil pressure acting to delay the release operation can be created.
The device may further comprise a choke arranged in the discharge hole or the drain path, and narrow an opening area thereof. Thus, path resistance can be increased to restrict passing of non-compressive oil with high viscosity through the purge path to allow selectively passing of compressive air with low viscosity through it. Moreover, since discharge of oil can be restricted, even when the lock member is in a locked state to restrict a rotation of the first and second rotors to open the purge path, consumption of oil in an oil-circulating system can be minimized to avoid a breakdown of the engine for the reason of a shortage of lubricating oil.
An opening area of the purge path may be wider than any opening area of the advance side pressure partition path, the retardation side pressure partition path and the release oil hydraulic supply path. Path resistance can be reduced to move up the sequence of supply of the oil pressure to the purge path.
The device may further comprise a choke of narrowing an opening area of the retardation side pressure partition path or the release oil hydraulic supply path. Thus, the major portion of the air-mixing oil can be discharged through the purge path rather than the retardation side pressure partition or the release oil hydraulic supply path.
An opening area of an oil path may be set by a relation of a pressure supply pathxe2x89xa7the purge pathxe2x89xa7a drain pathxe2x89xa7the release oil hydraulic supply path. Thus, the major portion of the air-mixing oil can be discharged through the purge path rather than the release oil hydraulic supply path. Moreover, discharge of non-compressive oil with high viscosity can be restricted in the drain path to allow selectively discharging of compressive air with low viscosity.
The device further comprise a valve having the advance side pressure partition path and the retardation side pressure partition path, wherein the valve may supply high oil pressure to the release oil hydraulic supply path, the supplied high oil pressure being selected from oil pressure in the advance side oil hydraulic pressure chamber and the retardation side oil hydraulic pressure chamber. Thus, air or air-mixing oil, which is used as a first pressure in a release operation on starting the engine, can be positively discharged to the outside. It is not necessary to use all the first pressure for the release operation, and the lock member can be released after applying oil hydraulic pressure which is able to control the valve timing control device. Therefore, it can prevent the occurrence of beat noise (abnormal noise).